2017 Volume 17 Issue 7 Pages 295-304
In recent years, a global shift has occurred with societies turning toward recycling. The looming problem of global warming has led to a significant increase in the use of biodiesel fuels made from vegetable fat and oil. In this regard, improvement of the waste recycling processes of the highly alkaline crude glycerol, which is by-product of biodiesel fuels, has received significant attention. Crude glycerol damages the incinerator during the incineration process and its purification via neutralization, desalination, and washing steps is very expensive. In our group, it was found that, without preprocessing, crude glycerol can be converted to biogas and other chemical materials via anaerobic digestion. In particular, it has been found that by using sewage sludge as seed materials and depending on the volume of crude glycerol, it is possible to switch between the methane and hydrogen fermentation processes. When the hydrogen fermentation process is predominant, 1,3-propanediol (1,3-PDO), a chemical raw material for the synthesis of polymers, is produced. Furthermore, in the research for fermentation promoters in glycerol digestion, it has been found that a small amount of glucose (less than 1% of the input amount of glycerol) promotes the growth of the hydrogen fermenting bacteria that are resistant to the highly alkaline conditions. Under high loads of glycerol, other mixed bacterial cultures are difficult to digest crude glycerol. However, the alkali-resistant bacteria promoted by glucose were able to successfully and efficiently convert glycerol to hydrogen. The co-digestion of food waste and crude glycerol has also been tested on a pilot scale. It was found that crude glycerol is a good input material as it acts as a pH adjuster and is also a source of carbon. This review summarizes the results of previous work performed our group and outlines the future prospects of the developed technology.
